Interpretive Summary: Neospora caninum is a major cause of abortion in dairy cattle worldwide. The fetus becomes infected by virtue of the parasite transferring from the mother via the placenta during specific times of gestation. The parasites arise in the mother from either a reactivated latent infection or by ingestion of parasite stages in the environment. Sheep were evaluated in the present study as a ruminant model for dairy cattle. The use of sheep would be to evaluate vaccines against neosporosis using a host that has a shorter gestation time and lower costs for animal husbandry. Six sheep were fed N. caninum oocysts, while two sheep served as uninfected controls. The infected sheep all contain parasites in circulating blood as early as 7 days after inoculation. Also, these infected sheep contained antibodies against the parasite. These results indicate that sheep are a suitable ruminant model for bovine neosporosis.

Technical Abstract:
Six ewes were fed 10,000 Neospora caninum oocysts, while 2 ewes served as uninoculated controls. All sheep were bled weekly for 7 wk after inoculation. Blood was analyzed for the presence of N. caninum DNA by 2 different PCR assays as well as for antibodies to recombinant and native N. caninum antigens. N. caninum DNA was detected in 2 sheep as early as 7 days after feeding oocysts (DAFO). All 6 sheep were PCR positive by 32 days and remained positive until the end of the study at 49 DAFO. Aside from 1 sheep, all sheep fed N. caninum oocysts contained detectable N. caninum DNA in brain tissue collected at 49 DAFO. Antibodies were detected by enzyme-linked immunosorbent assay, Neospora agglutination test, or immunoblotting to either native or recombinant N. caninum antigens in sheep fed oocysts.